Precision servo control system for a pneumatic actuator

Abstract

A precision servo control system for a pneumatic actuator has a piston positionable over a stroke of the pneumatic actuator using a supply of pressurized gas. A brake and a sensor system are connected to the actuator and to the servo control system. The servo control system operates to initiate the forward thrust from the pressurized gas to move the piston along the stroke. When a braking point along the stroke is determined, the servo control system initiates a reverse thrust from the pressurized gas while maintaining the forward thrust and simultaneously begins to selectively apply the brake to stop the piston within a predetermined tolerance of a desired stopping position.

What is claimed:  
     
       1. A precision servo controlled pneumatic actuator comprising: 
       a pneumatic actuator having a positionable component with a stroke length; and  
       a servo control system operably connected to said pneumatic actuator, wherein said servo control system operates in accordance with a pre-established motion profile to repeatably position said positionable component within a predetermined tolerance at a plurality of programmable positions along said stroke length, wherein said servo control system is programmed with a system of gain parameters, wherein said servo control system performs an adjustment routine to determine an optimal set of said system gain parameters, and wherein said servo control system utilizes said optimal set of gain parameters to modify said pre-established motion profile to an optimal motion profile.  
     
     
       2. The pneumatic actuator of  claim 1 , wherein said stroke length is equal to or greater than twenty-four (24) inches. 
     
     
       3. The pneumatic actuator of  claim 1 , wherein said predetermined tolerance is a fixed value of more precise than +/−0.1 inches regardless of stroke length. 
     
     
       4. An automated method of controlling a pneumatic actuator operably connected to a piston in a chamber and to a brake wherein a sensor system generates measurement values representative of a movement of the piston, the method comprising: 
       providing a servo control system that operates to repeatably position to piston; and  
       programming the servo control system utilizing a set of standard loop gain parameters of a servo system for an electrically powered actuator including a proportional gain, (KP); an integral gain, (KI); and a derivative gain, (KV), and one additional control parameter beyond the standard control loop gain parameters of the servo system for said electrically powered actuator wherein said one additional control parameter is a deceleration current constant gain, (KT) that is used to set a minimum brake control signal while the brake is decelerating a load carried by the piston.  
     
     
       5. The method of  claim 4 , further comprising using a deceleration compensation path that enters into effect after a deceleration point, wherein the deceleration compensation path uses the deceleration current constant gain, (KT) to adjust for position overshoot, position undershoot, and deceleration profile linearity when the piston approaches a target position. 
     
     
       6. A method of controlling a pneumatic actuator operably connected to a piston in a chamber and to a brake wherein a sensor system generates measurement values representative of a movement of the piston, the method comprising: 
       providing a servo control system that operates to repeatably position the piston in accordance with a pre-established motion profile; and  
       programming the servo control system utilizing a set of system gain parameters;  
       performing an adjustment routine to determine an optimal set of the system gain parameters and  
       automatically utilizing said optimal set of the system gain parameters to modify said pre-established motion profile to an optimal motion profile.  
     
     
       7. The method of  claim 6 , wherein the adjustment routine comprises: 
       specifying a bore size and a usable stroke length of the pneumatic actuator;  
       cycling the piston to positions between ends of the usable stroke length while using a plurality of projected sets of servo parameters; and  
       selecting one of the projected sets of servo parameters that achieves a best result of positioning the piston.  
     
     
       8. The method of  claim 7 , further wherein cycling step is repeated between 6 to 15 cycles. 
     
     
       9. The method of  claim 7 , wherein the selecting step automatically evaluates at least three factors: 
       an overshoot of the position of the piston;  
       an undershoot of the position of the piston; and  
       a velocity following error (overshoot/undershoot)  
       wherein the selecting step operates to minimize these factors.